This invention relates, in general, to gain stages, and more particularly, to switched capacitor gain stages.
An amplifier typically has an input and an output. The amplifier amplifies a signal applied to the input and provides the amplified signal at the output. In general, amplifiers are characterized by the amount of gain or amplification provided, bandwidth or frequency of operation, noise characteristics, and accuracy of amplification. Amplifiers are commonly used in many different types of circuits, for example, Analog to Digital converters.
One type of amplifier is a switched capacitor amplifier. A switched capacitor amplifier is a clocked circuit that operates in discrete steps. For example, in a first phase of a clock cycle a voltage is sampled, in particular, capacitors of a switched capacitor amplification stage are charged to the voltage. Switches are used to couple the capacitors in different configurations. The switches are transmission gates formed from complementary transistor types. In a second phase of a clock cycle, the capacitors of the switched capacitor amplifier are coupled via switches around an amplifier in a configuration to amplify a sampled voltage. The voltages stored on the capacitors in the first phase of the clock cycle determine the magnitude of an output voltage of the amplification stage. The gain is typically fixed by the amplification stage configuration (in the second phase of the clock cycle) and the capacitor values.
In general, the operational speed of a switched capacitor amplifier stage is limited by the time needed to charge and discharge capacitors of the amplifier stage or the time required for an amplifier of the amplification stage to stabilize. For example, switched capacitor gain stages are used in pipelined Analog to Digital Converter (ADC) stages. The switched capacitor gain stages are used in a pipelined ADC to amplify an analog signal. An output of a switched capacitor gain stage in an ADC corresponds to a digital equivalent of an analog signal level. The speed or frequency at which an analog signal can be converted to a digital signal is directly related to the speed of the switched capacitor amplifier stages. An increase in the speed of switched capacitor amplifiers stages of an analog to digital converter can be used to enhance the frequency of operation.
It would be of great benefit if a switched capacitor amplification stage could be provided that decreases the time needed to amplify a signal.